A conventional exchange does not have a call supervisory system performed by a function of the exchange itself. Conventionally, technology of call monitoring and tapping is embodied in a manner that connects lines in a physical speech path in parallel, but there does not exist a function of monitoring and tapping calls according to a control of a relevant exchange itself. The function of monitoring and tracking subscriber's calls exists just for maintenance and repair of the exchange, and the function of tapping the calls exists just for testing a subscriber line. The two functions generally exist individually.
Each conventional function has been developed just for maintenance and repair of the exchange, which does not satisfy an objective of the call supervisory system for performing call tracking, call monitoring and call tapping through one connected functional operation. In addition, the conventional call tracking function does not have a feature of tracking calls of prefix which is required in the call supervisory system, and the conventional call monitoring function cannot perform the call tapping function simultaneously when the call is made. The conventional call tapping function cannot be performed without use of a test device, and a single test device allows tapping only one per 4096 subscribers. This causes a capacity problem, and the conventional art does not allow both call monitoring and call tapping functions to be performed simultaneously.
After all, in the conventional exchange, the call supervising function is performed only on the speech path, and there does not exist the call supervisory system falling under a function of the exchange itself.